From the E.P.A.

You may never see a mouse or rat unless an infestation is severe. Look for signs of rat or mouse infestation:

• Rodent droppings around food packages, in drawers or cupboards, and under the sink.
• Nesting material such as shredded paper, fabric, or dried plant matter.
• Signs of chewing on food packaging.
• Holes chewed through walls and … Read more